The present invention relates to a storage system for use by a computing system.
JP-A-9-297699 (pages 3-4 and FIG. 1) discloses a system referred to as a hierarchical storage system which comprises a computer, and a high speed storage and a low speed storage connected to the computer. In JP-A-9-297699 (pages 3-4 and FIG. 1), more frequently used files are stored in a high speed storage such as a magnetic disk drive, while less frequently used files are stored in an inexpensive low speed storage such as a tape drive. Then, a table is used to manage the access frequency for each file, and is referenced to determine which file is allocated to or stored in which storage.
JP-A-9-297699 relies on software running on the computer to implement a hierarchical storage control for moving a file between a small capacity magnetic disk drive and a large capacity magnetic tape drive in accordance with how frequently the file is used. The hierarchical storage control assumes that data which has been highly frequently accessed in the past will be highly frequently accessed as well in the future, and determines a storage for storing data therein in accordance with statistic information on the access frequency of the data and an available capacity of a fast accessible storage. Then, the hierarchical storage control improves the processing efficiency and practically manages a large amount of files by increasing the probability that highly frequently accessed data is stored in a fast accessible storage.
The conventional hierarchical storage technique, however, has a problem in that the capacity scalability is limited by the number of magnetic disk drives and the number of magnetic tape drives which can be connected to the computer, thereby failing to fully provide long-term management for a large amount of information which increases more and more over time.